Generally a magnetic read head includes a pair of upper and lower magnetic shield layers, a magnetoresistive film disposed therebetween, and a pair of electrodes connected electrically to the magnetoresistive film. In the case of magnetic recording and reproducing apparatus having an areal recording density in excess of 300 Gbits per 1 square inch, a high sensitive read device such as a tunneling magnetoresistive film (TMR film) or a current-perpendicular-to-plane giant magnetoresistive film (CPP-GMR) is utilized as a magnetoresistive film. The magnetoresistive film has a free layer, an intermediate layer, and a pinned layer, in which the magnetization in the free layer rotates in accordance with the change of signal magnetic fields from a recording medium. On the other hand, the direction of the magnetic moment in the pinned layer is generally fixed. When a sense current is supplied to the magnetoresistive film, a voltage between electrodes of the device changes depending on the angle formed between the magnetic moment of the free layer and the magnetic moment of the pinned layer. The resulting voltage is detected as a read signal. In the CPP-GMR film, the intermediate layer is a conductor and an oxide or the like is used in the TMR film.
In the magnetic read head, a magnetic domain control film is disposed on both ends in the direction of the track width of the free layer for making the free layer into a single magnetic domain structure or preventing magnetic domain movement. This configuration aims at preventing erroneous operation of the recording and reproducing apparatus caused by output fluctuation or the like due to movement of the magnetic domain in the case where the magnetic domain of the free layer undergoes a magnetic effect from the write element, upper and lower magnetic shields, etc. For such a magnetic domain control film, a permanent magnet is generally used (see Japanese Patent Publication No. 3-125311 “Patent Document 1”). On the other hand, In the case of the TMR film or the CPP-GMR film, it has also been proposed to adopt a structure in which a magnetic domain control film is stacked to a ferromagnetic free layer. In this case, as the magnetic domain control film, a permanent magnet (see Japanese Patent Publication No. 11-259824 “Patent Document 2”) or a stacked layer of an anti-ferromagnetic layer and a ferromagnetic layer (see U.S. Pat. No. 6,023,395 “Patent Document 3”) has been known.
To increase the density of the magnetic recording and reproducing apparatus, it is useful to narrow a recording bit and, for coping therewith, it is requested to narrow the distance between upper and lower magnetic shields of the magnetic read head and the read track width thereof.
As described above, to improve the recording density of the magnetic recording and reproducing apparatus, the read track width of the magnetic read head has been finely formed. Generally, the read track width is narrower, the read output is lowered. Further, it has been pointed out that magnetization fluctuation noises become actual as the read device is made finer. The magnetization fluctuation noise is caused by thermal fluctuation of magnetization in the free layer. Generally, as the volume of a magnetic body decreases, thermal fluctuation of magnetization increases. Accordingly, as the device is made finer, the volume of the free layer is decreased to increase the thermal fluctuation of magnetization in the free layer. Then, a relative angle between the magnetization in the free layer and the magnetization in the pinned layer fluctuates greatly, resulting in increased noise. Further, it has a characteristic that the magnetization fluctuation noise increases in proportion to the output. This means that unless the magnetization fluctuation noise per se is suppressed, improvement for a signal-to-noise ratio cannot be expected even when the output is merely increased.